Various methods are used for defect detection and length measurement and shape evaluation in a formation of a microcircuit such as an LSI. For example, with an optical test device, optical images of the microcircuit are generated and the images are tested for abnormality detection. However, these optical images have resolution that is insufficient to permit identification of very small shape features, and cannot satisfactorily perform distinction between a harmful defect and a harmless defect upon the circuit formation. A target sample of such a measurement and test device has been increasingly miniaturized following technical advancement, and for example, in a process of manufacturing a latest DRAM, a linewidth of a metal wire reaches 40 nm or below, and a logic IC has reached a gate dimension of 20 nm.
A defect test method by use of an electron beam is provided with sufficient resolution for imaging minute shape features of a contact hole, a gate, and wiring and shape features of a minute defect, and can be further used for classification and detection of a severe defect based on a shade image contrast of the defect shape. Therefore, for measurement and test of the microcircuit, a measurement and a test method putting a charged particle beam into practical use is considerably more advantageous than an optical test method.
A scanning electron microscope (SEM) as one of charged particle beam apparatuses focuses a charged particle beam emitted from an electron source of a heating type or an electric field discharge type to form a thin beam (probe beam), and scans this probe beam on a sample. Through this scanning, secondary charged particles (secondary electron or reflection electron) are generated from the sample, and providing these secondary charged particles as a luminance signal of image data in synchronization with the scanning of the primary charged particle beam provides a scanned image. In a typical scanning electron microscope, with an extraction electrode between the electron source to which a negative potential has been applied and a grounding potential, the electron emitted from the electron source is accelerated and irradiated to the sample.
There is a close relationship between resolution of a scanning type charged particle microscope such as the SEM and energy of the charged particle beam. Arrival of the primary charged particle beam with high energy at the sample (that is, great landing energy of the primary charged particle beam) causes the primary charged particle to enter deeply into the sample, thus widening a range of emission of the secondary electron and the reflection electron on the sample. As a result, the range of emission becomes wider than the probe size of the charged particle beam, resulting in remarkable deterioration in observation resolution.
In contrast, reducing energy of the primary charged particle beam too much in order to reduce the landing energy results in a remarkable increase in the probe size of the charged particle beam due to aberration of an objective lens, deteriorating the observation resolution.
To perform observation with high resolution, energy of the primary charged particle beam, the landing energy in particular, needs to be appropriately controlled in accordance with an observation target.
As a technology of controlling the landing energy, a retarding method is widely used. Specifically, with the retarding method, such a potential that decelerates the primary charged particle beam is applied to the sample to reduce the energy of the charged particle beam to desired energy immediately before arrival at the sample. However, as soon as the charged particle beam is inclined towards a sample to be observed, observation with high resolution can no longer be performed.
Disclosed in Patent Literature 1 is, as a technology of inclining a charged particle beam with respect to a sample to be observed while maintaining high resolution condition of an apparatus, late race on an electron optical orbit in, for example, a method of using focus operation of an objective lens by making the charged particle beam enter to outside of an axis of the objective lens.
Moreover, disclosed in Patent Literature 2 is a technology of correcting off-axis chromatic aberration occurring when two stages of deflection means adapted to deflect a charged particle beam in mutually opposite directions within a focus magnetic field of an objective lens are provided and the charged particle beam is inclined outside an axis of the objective lens.
Moreover, disclosed in Patent Literature 3 is a technology of performing correction with a Wien filter in which two stages of deflection means for passage of a charge particle beam through outside of an axis of an objective lens are provided closely to an electron source than the objective lens to thereby reduce resolution deterioration occurring upon inclination of the charged particle.
Further, disclosed in Patent Literature 4 is a technology of providing, in addition to deflection means within a focus magnetic field of the objective lens, a cup-shaped electrode for beam deceleration between the objective lens and a sample to thereby increase a beam inclination angle.
In addition, disclosed in Patent Literature 5 is an invention in which an orbit of a primary beam is caused by a deflector or a movable diaphragm to pass through outside of an axis and controlling its off-axis orbit to cancel aberration occurring on the objective lens at time be beam inclination by use of aberration of another lens.